Procurement Change Orders

We are looking at switching change orders on in Procurement, although already using order revisions, which we use to control PO printing options.

When we set the processing option on to protrect the base order, the system does not allow me to enter a change order.

I found reference to the line number in doc 625539.1, however nothing about SFXO

My understanding is that using change orders in conjunction with order revisions should allow changes to all SFXO's but each being treated as a seperate order in its own right, can someone clarify this.

Secondly, has anyone come across the issue with the base order protection processing option stopping all changes to the order?